Biochemical characterization of a 22-kDa high affinity antiischemic drug-binding polypeptide in the endoplasmic reticulum of guinea pig liver: potential common target for antiischemic drug action.

Abstract	The phenylalkylamine emopamil prevents brain damage due to experimental cerebral ischemia. Stereoselective, high affinity, binding sites for (-)-[3H]emopamil in guinea pig brain cortex and liver membranes have been proposed to mediate its antiischemic effect. Using [N-methyl-3H]LU49888 as a photoaffinity probe we now provide evidence that the cation-sensitive emopamil binding site is localized on a 22-kDa polypeptide in guinea pig liver, kidney, lung, and adrenal gland. This 22-kDa polypeptide binds other antiischemic drugs with high affinity and is a nonglycosylated integral membrane protein of the endoplasmic reticulum. It can be solubilized with digitonin without changes in its drug-binding properties. The solubilized binding activity has a sedimentation coefficient of 12.0 +/- 0.4 S and an apparent Stokes radius of 6.0 +/- 0.1 nm. From these data it is concluded that the 22-kDa polypeptide is associated in a larger oligomeric complex with a molecular mass of at least 84 kDa. [N-methyl-3H]LU49888 also specifically labels a second 27-kDa polypeptide in the endoplasmic reticulum, which can be distinguished from the 22-kDa polypeptide by its pharmacological and hydrodynamic properties. The photolabeled 22-kDa polypeptide was partially purified under denaturating conditions. This will allow the further structural analysis of this putative target for antiischemic drugs.
Authors	F F Moebius, G G Burrows, J Striessnig, H Glossmann
Journal	Molecular pharmacology (Mol Pharmacol) Vol. 43 Issue 2 Pg. 139-48 (Feb 1993) ISSN: 0026-895X [Print] United States
PMID	8429820 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)
Chemical References	Affinity Labels Membrane Proteins Receptors, sigma Verapamil emopamil
Topics	Affinity Labels Animals Binding Sites Binding, Competitive Endoplasmic Reticulum (metabolism) Female Guinea Pigs In Vitro Techniques Ischemia (drug therapy) Liver (metabolism) Male Membrane Proteins (isolation & purification, metabolism) Molecular Weight Photochemistry Radioligand Assay Receptors, sigma (metabolism) Solubility Verapamil (analogs & derivatives, metabolism)

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